In recent years, there have been used, as a cooker for household or business use, an infrared heating cooker using a radiant heater or a halogen heater and an induction heating cooker, in place of or together with a conventional gas cooker or the like using a gas range.
As a top plate used for each of those cookers, a heat-resistant substrate made of a non-metal material typified by crystallized glass is used because of being excellent in heat resistance, aesthetic quality, ease of cleaning, or the like. The crystallized glass is particularly suited to a top plate for a cooker because stains, such as oil of food materials or water stain stuck on the crystallized glass may relatively easily cleaned.
Further, besides the top plates for a cooker, a heat-resistant substrate made of crystallized glass, or the like, is used for glass articles, such as a shelf plate of a microwave oven, a window of a stove, or a fireproof window, which becomes high in temperature during its use.
By the way, there is generally known a method for forming a hydrophilic film such as a silica film or a resin film on surfaces of glass articles, such as the top plate for a cooker described above for protections of flaws and for imparting antifouling property. However, there is a problem in that the silica film is easily degraded by an alkaline detergent, and the resin film is easily degraded by an acidic or alkaline detergent. Thus, there is disclosed an antifouling film containing a multiple oxide of silicon and zirconium or a mixture of a silicon oxide and a zirconium oxide as a hydrophilic antifouling film which is highly durable against various detergents (see, for example, Patent Document 1).